Flight 90: Released from Alamogordo, New Mexico, 1502 MST, August 27, 1948 Recovered at Roswell, New Mexico
The .001" , 20-foot polyethylene balloon used on this flight was released in mid-afternoon to provide a test of the sunset effect on a balloon supported by the automatic ballast valve.
From the height-time curve, Figure 40, it may be seen that the balloon had attained a floating altitude shortly before the sunset and that the action of the automatic ballast valve was sufficient to restore the buoyancy
Figure 40
and cause the balloon to again reach a floating condition. The difference between the two floating levels may be explained by a consideration of the automatic ballast valve and the minimum-pressure switch which was used to seal off its aneroid capsule. Since the balloon had not fallen far enough to permit the switch to seal off the valve before sunset, this action was accomplished